Hydrocarbon wells such as oil and gas wells frequently need fracturing of the strata to adequately produce hydrocarbons from the strata. Fracturing cracks the strata to allow more surface area to flow the hydrocarbons. Fracturing generally occurs after the well has been drilled, casing has been placed, and various completion tools inserted into the well bore. Proppant through a flowable slurry is filled in the cracks to maintain the cracks in an open position. A screen is typically placed in the well bore to allow hydrocarbons to flow into a production tubing and up to the well surface without allowing the proppant and sand from the strata to flow into the tubing.
The typical techniques involved in flowing proppant are to flow it through a central flow path in a tubing string disposed in the casing and divert it to an annulus formed between a completion assembly, attached to the tubing string, and the casing to fill the annulus in the region of the screen. Then, the flow path is reversed to wash out excess proppant remaining in the tubing string and a cross-over tool.
To accomplish the flow reversal, the cross-over tool is frequently used by attaching it to the tubing string above the screen region. The cross-over tool is positioned in the completion assembly so that the slurry is initially diverted from the central flow path of the tubing string into the annulus around the screen and into the formation. The flow reversal can occur by repositioning the cross-over tool to the reverse position to create a flow path down an upper portion of the annulus and back up the central flow path of the tubing string.
A problem has been realized in the flow reversal. The frac pressures used to treat the well can actually stretch or contract the tubing string, known as tubing movement. Tubing movement can occur by temperature changes, piston effects, ballooning effects, buoyancy effects, and other downhole conditions. A typical length of several thousand feet of tubing that is often placed in the well bore can change length based on the above factors. The tubing movement length change can cause misalignment of the tool structures and inadvertently open and close ports that are not intended. Inadvertently open flow ports can cause the proppant placed in the fracturing operation to become displaced and create other disadvantageous results.
For example, if the cross-over tool is in the reverse position, a so-called circulating valve needs to remain closed. If the valve opens, reverse fluid can travel through the circulating valve, out a wash pipe in the completion string, through the screen, and into the frac pack. Fluid movement upward through the pack tends to “fluff” the pack, thus, destroying the integrity of the pack by creating voids. This upward flow can also carry sand or proppant back into the tool assembly, creating other problems. Stated differently, the circulating valve, or in some cases, a reversing ball, must not open while reversing. But if tubing movement enables fluid communication, then “fluffing” can occur.
Other problems can also occur from inadvertent opening and closing, such as loss of fluids or misdirected fluids at inappropriate times, and so forth. Further, tubing movement exists with other procedures, such as gravel packing, acidizing, water packing, and other well treatments and can also cause problems.
Therefore, there remains a need to increase the reliability of the fracturing operation and other well treatment operations.